1. Field of the Invention
The present invention relates to a process for the viscosification of an aqueous acid solution which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 100 cps; dissolving a neutralized or unneutralized sulfonated polymer (water insoluble) in the solvent system to form a solution, a concentration of the neutralized sulfonated polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent of the aqueous acid solution the aqueous acid solution being immiscible with the organic liquid and the polar cosolvent and neutralized sulfonated polymer transferring from the organic liquid to the aqueous acid phase, thereby causing the aqueous acid phase to gel.
2. Description of the Prior Art
There are many applications for very viscous or gelled solutions of polymers in water which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for gelling (i.e. thickening) an aqueous acid solution by contacting the aqueous acid solution with a relatively low viscosity, organic liquid solution of an ionic polymer.
The instant invention differs from a number of applications, Ser. Nos. 223,482; 136,837; and 106,027, filed by Robert Lundberg et al, one of the instant inventors. These previously filed applications were directed to the gelling of the organic liquid by a water insoluble, neutralized sulfonated polymer whereas the instant invention is directed to the gelling of an aqueous acid solution. Quite unexpectedly, it has been discovered that when the concentration of the sulfonated polymer in solution is maintained in a critical concentration range of 0.01 to 0.5 weight percent of the total volume of solvent, which is a mixture of nonpolar organic liquid and a polar cosolvent, upon the addition of aqueous acid solution, a transfer of the polar solvent and water insoluble neutralized sulfonated polymer from the nonpolar organic liquid phase to the aqueous acid phase occurs. The water insoluble neutralized sulfonated polymer causes the aqueous acid phase to gel, wherein the neutralized sulfonated polymer is insoluble in the aqueous acid phase. In the previously filed patent applications, substantial viscosification of the nonpolar organic liquid phase did not occur until the concentration of the neutralized sulfonated polymer was sufficiently high enough to permit chain entanglement of adjacent polymer molecules thereby completely filling the solvent space. The gelation of the aqueous acid phase of the instant invention does not occur by this previously described mechanism because the resultant concentration of water insoluble, neutralized sulfonated polymer is not sufficiently high enough to permit chain entanglement. The mechanism of gelation of the aqueous acid phase, as defined in the instant invention, occurs by the formation of macroscopic spherical polymer membranes or films dispersed throughout the aqueous acid phase, wherein large volumes of the aqueous acid are encapsulated within a series of minute polymer bags (i.e. pseudo-emulsion).
The instant invention describes a process which permits (1) the preparation of polymer solutions of sulfonated polymers in organic liquid having reasonably low viscosities (i.e., less than about 200 cps); and (2) the preparation of extremely viscous solutions or gels of an aqueous acid from such solutions by a process of mixing or contacting an aqueous acid solution with the polymer solution. These operations are achieved by the use of the appropriate concentration; 0.01 to 0.5 weight percent of water insoluble, neutralized sulfonated polymers, having low concentrations of ionic groups present, preferably metal sulfonate groups. Such polymers are described in detail in a number of U.S. Patents (U.S. Pat. Nos. 3,836,511; 3,870,841; 3,847,854; 3,642,728; and 3,921,021) which are herein incorporated by reference. These polymers possess unusual solution characteristics some of which are described in U.S. Pat. No. 3,931,021. Specifically, these polymers, such as lightly sulfonated polystyrene, containing about 2 mole percent sodium sulfonate pendant to the aromatic groups, are typically not soluble in solvents commonly employed for polystyrene itself. However, the incorporation of modest levels of polar cosolvents permit the rapid dissolution of such ionic polymers to form homogeneous solutions of moderate viscosity.
In the instant process, the role of the polar cosolvent is that of solvating the ionic groups while the main body of the solvent interacts with the polymer backbone. For example, xylene is an excellent solvent for the polystyrene backbone and when combined with 5 percent methanol will dissolve, readily and rapidly, the previous example of lightly sulfonated polystyrene.
The remarkable and surprising discovery of the instant invention is that when small (or large) amounts of an aqueous acid solution are combined and mixed with solutions of ionic polymers dissolved at low concentrations (0.01 to 0.5 weight percent) in such mixed solvent systems as those described above, a phase transfer of the water insoluble, neutralized sulfonated polymer and cosolvent occurs from the nonpolar organic liquid phase to the aqueous acid phase, wherein the aqueous acid phase gels. Indeed, it is possible to achieve increases in viscosity of the aqueous acid phase by factors of 10.sup.3 (1,000) or more by the addition of only 5 to 15 percent aqueous acid based on the polymer solution volume. This unusual behavior is postulated to arise from the removal of the polar cosolvent and water insoluble, neutralized sulfonated polymer from the organic liquid phase into the separate aqueous acid phase which then gels (i.e. thickens).